The present invention relates to a device and to a process for the automatic measurement and recording of the permeability of solid samples, such as cores of mineral materials obtained from drill-holes in the ground.
Knowledge of the permeability of a rock is an important parameter for assessing the capacity of a fluid, namely a gas or a liquid, to circulate in the pores of the component material of the rock.
For many years, the permeability of rocks was measured manually by means of conventional permeameters, entailing the constant presence of an operator to monitor a pressure difference to be applied between the end faces of the generally cylindrical sample and to measure the flow time of a certain volume of fluid through the said sample, the fluid usually being a gas.
Measuring the transit time of a known volume of gas through the sample makes it possible, by applying Darcy's Law, to determine the permeability of the sample being studied.
To overcome the disadvantage of carrying out the abovementioned measurements manually, a process and a device, such as are described in French Pat. No. 1,388,740, have been proposed. The process involves transferring in sequence each of the samples to be studied from a pile arranged in a feed chute towards a measuring cell comprising a diaphragm capable of being deformed so as to seal off the lateral face of the sample introduced into the said cell, isolating one of the end faces of the sample from the ambient atmosphere, passing a gas stream at a given pressure through the sample from the isolated face, and then measuring the transit time of a predetermined volume of gas through the sample.
The process briefly described above and the device for carrying it out have two serious disadvantages.
The first is that each sample to be studied falls into the master cylinder as a result of gravity, before being pushed into the measuring cell, and such a fall can cause damage to the said sample and generate dust which has to be eliminated and prevented from being introduced into the measuring cell, failing which the sample could not be sealed off laterally in an effective way and the measurement would be subject to error.
The second disadvantage is much more important if the measurement is to be made fully automatic. In fact, the type of material varies from one sample to another, and consequently the permeability values to be measured vary within a range between 0 and 6 Darcys. Under these conditions, if a suitable permeability value is not obtained for a given pressure difference and a given gas volume, the pressure difference to be applied between the faces of the sample and the volume of gas introduced have to be readjusted by hand.
It will be appreciated that such a device is not suitable for appropriate automation of the permeability measurements.
The main subject of the present invention is an automatic device for measuring the permeability of a large number of samples in a relatively short time.
The process according to the invention is characterized in that it involves applying a constant differential pressure between the end faces of the sample which are arranged in a measuring cell, introducing a pressurized gas into the said sample for a constant time, measuring the fluid flowrate, and then calculating the permeability of the said sample by applying Darcy's Law.
One advantage of the present invention is that the pressure difference applied to the two faces of the sample is adjusted automatically as a function of the measured fluid flowrate, so as to obtain as accurate a permeability value as possible.
Another advantage is that the samples are introduced into the measuring cell automatically and in sequence, the sample being guided constantly during its movement. Other advantages and characteristics will emerge more clearly from a reading of the description of a preferred embodiment given as an illustrative, but non-limiting example, and from the attached drawing in which: